Lined corrosion resistant pump



LINED CORROSI Filed Jan. 22, 1969 J. L'. wlsswm ON RESISTANT PUMP 3Sheets-Sheet 1 INVENTOI? JACK L. WISSMAN ATTORNEYS Dec. 29, 1970 J w 5 I3,551,067

LINED CORROSION RESISTANT PUMP Filed Jan. 22, 1969 5 Sheets-Sheet 2 nosF G 6 m8 :Inu

Dec. 29, 1970 w 55 LINED CORROSION RESISTANT PUMP Filed Jan. 22, 1969 5Sheets-Sheet 3 FIG-9 United States Patent O York Filed Jan. 22, 1969,Ser. No. 792,938 Int. Cl. F01d 1/02, 9/00, 25/26 US. Cl. 415-134 14Claims ABSTRACT OF THE DISCLOSURE A pump includes a casing and coverassembly forming a chamber having an inlet and an outlet. The fluidcontacted surfaces of the casing and cover assembly are sheathed withpolytetrafluoroethylene, the sheaths including neck portions extendingthrough the inlet and outlet and being flanged for mounting conduits inthe usual way. A driven impeller is positioned within the chamber, andall fluid contacted surfaces of the impeller are covered withpolytetrafiuoroethylene. The sheaths include peripheral portions clampedbetween the casing and cover assembly to provide a seal therebetween,these peripheral portions being secured against movement radiallyinwardly. The inner periphery of the sheath covering the cover is alsosecured against radially inward movement.

BACKGROUND OF THE INVENTION The present invention relates to pumps andmore particularly to an improved centrifugal pump for use with corrosivematerials wherein the pump chamber is fully sheathed withpolytetrafluoroethylene, and wherein the impeller is a corrosionresistant material or is also covered with corrosion resistant coatingof polytetrafluoroethylene.

It is known to form pump parts of solid or filledpolytetrafluoroethylene (PTFE), see for example US. Pat. No. 2,880,676of April 1959 and U.S. Pat. No. 2,966,860 of January 1961.

It is also known to use a copolymer of a fluorocarbon resin to form alining on a pump chamber. In the latter structure, the internal surfacesof the chamber include anchoring or locking apertures which receivelocking lugs on the outside surface of the liner, the liner being ofmaterial such as fluorinated ethylene propylene. The purpose of thelocking lugs and apertures is to prevent movement of the liner inresponse to increases in temperature. PTFE being more like athermosetting resin as opposed to the fluorinated copolymers which arethermoplastic, does not require locking lugs or apertures to maintain astable configuation over a range of temperatures, e.g., F. to +400 F.

The processing of fluorinated copolymers is quite different from thatused with PTFE in that the latter has a plastic memory which tends tocause the part to revert to is originally formed shape when heated in anunconfined condition. For example, a part of PTFE which has beensintered can be hot or cold worked to change its shape, but once heatedin an unconfined state, the part tends to revert to its originalsintered shape. If unconfined and heated to the range of 700 to 750 F.,a hot or cold worked part will revert to its sintered configuration. Inits original sintered form the part has a primary memory of that shape,and once worked, the part has a secondary memory of its worked shape.Thermoplastics do not have both a primary and secondary memory as doesPTFE. The secondary memory may create difliculty because temperaturecycling can cause sufficiently serious distortion of the part to renderit useless for its designed purpose.

In pumps used in the chemical process industry there are several generalfactors which are usually considered in the design of a pump, asfollows: (1) pump parts, espe 3,551,067 Patented Dec. 29, 1970 "icecially the wet end must be of corrosion resistant alloys, (2) mechanicaldesign must take into account the physical characteristics of the alloy(3) the wet end should be interchangeable so that dilferent wet ends maybe used with different chemicals and (4) the pump should be eflicient inits operation.

The corrosion encountered in the pumps in the chemi cal processingindustry may be of various types, such as:

(a) Chemical corrosion, i.e., nitric acid on bronze or hot sulfuric acidon Type 304 steel;

(b) Pittingbelieved to be failure of alloy to form the resistant oxidefilm;

(c) Galvanicuse of dissimilar materials and electro chemical corrosionof the part which is the anode;

(d) Concentration corrosion-local corrosion where small pockets ofliquid are trapped;

(e) Erosionmechanical destruction by high velocity materials or slurry;

(f) Fatigue corrosion-a combination of the above;

(g) Dezincificationzinc is leached from the alloy and deposited backelectrolytically; and

(h) Intergranular corrosionthe formation of chro mium carbide around aportion of the grains in stainless steels.

Apart from the question of corrosion resistance, there are several otherfactors which are considered in the design of a pump, such as:

(a) The pump should not act as a source of contamination for the fluidbeing pumped, e.g., pumps for use in the food and beverage field, thepharmaceutical industry and certain types of service in the chemicalprocess industry;

(b) Non-adherent wet ends, i.e., the wet end is designed so that thematerial pumped does not adhere thereto; and

(c) Non-sparking due to metal-to-rnetal contact of parts in the wet endof the pump.

The design of pumps and interchangeability of wet end parts has been animportant factor because of the variety of services in the chemicalprocessing industries and the recognition that some of the alloys do notlend themselves to certain designs or service. Other factors are theperformance of the pump, usually expressed in various ways, for example,gallons pumped per minute, total head in feet, net positive suctionhead, etc. It is a real advantage to be able to provide a pump usablefor different types of services so as to eliminate the need forinterchangeable wet ends. Where such a pump can be provided by utilizingthe easy to machine alloys which provide good mechanical strength, anadditional practical advantage exists. As a general rule, the corrosionresistant alloys customarily used are either diflicult to machine ordiflicult to cast. A corrosion resistant pump of easily cast andmachined alloys which maintains good operating parameters, especiallyone capable of being used with several different types of chemicalsoffers a real practical advantage by avoiding a substantial number ofproblems.

SUMMARY OF THE INVENTION In accordance with the present invention, apump of the centrifugal type is provided in which all fluid contactedsurfaces of the pump chamber are coated with a relatively thin coatingor liner of PTFE, the liner being sufliciently thick to prevent passageof corrosive materials therethrough while being sufficiently thin to becharacterized as a coating orliner. The chamber is formed by a casingand cover assembly each sheathed with a liner of PTFE, the liner alsoacting as a seal between these parts. The chamber is provided with aninlet and an outlet, also sheathed in PTFE, each of the inlet and outletpassages including a flange of PTFE which is integral with theassociated sheath or liner thereby forming a seal with the attachedpiping.

Received within the chamber is an impeller which is also corrosionresistant, i.e., sheathed or lined with PTFE to form an encapsulatedimpeller, or of a corrosion resistant metal such as titanium, zirconium,or epoxy resin and the like. The impeller is driven by a shaft whichpreferably includes a PTFE sleeve thereon, and in the case of anencapsulated impeller, integrally formed with the coating of theimpeller proper, a seal being provided between the cover and the shaft.The sheaths on the casing or cover assembly include peripheral portionsin facing sealed relationship, and means are provided to secure theseperipheral portions of the sheaths against radially inward movement inresponse to temperature cycling or relief of residual stresses in thispart of the sheaths. The sheath which covers the casing also includes aninner peripheral portion securely anchored against radially inwardmovement. Because the sheaths are originally formed and sintered in aconfiguration generally corresponding to the configuration of the partwith which they are associated, and since the sheaths are securelyanchored relative to the parts to which they are associated, the sheathsremain in a stable configuration over a wide temperature range.

One of the features of the present invention is the provision of asheath or liner of corrosion resistant substantially chemically inertplastic material which possesses exceptional temperature stability overa wide range of temperatures, e.g., 20 to +400 F. This is achieved byforming a sheath of PTFE so that the major portions thereof are formedin a configuration essentially that of its final configuration.Specifically, the portions of the sheath which are contacted by fluidare formed and sintered in a configuration corresponding essentially tothat which the part has in the assembled pump. Since PTFE has a primarymemory which is stable over the entire useful temperature range of thepart, there is little tendency for the portion contacted by fluids tochange shape. In other words, the portions of the sheaths contacted byfluid behave like a thermosetting resin to the extent that they possessa primary memory of their sintered and assembled configuration. Sincethe portions of the sheath which come in contact with fluid are not hotor cold worked they do not have a secondary memory of a shape differentfrom that in which they were formed.

There are portions of the sheaths which do have a secondary memory,i.e., the peripheral portions, and these are clamped in place so thatmovement thereof is substantially eliminated, as previously noted.

Self-priming centrifugal pumps may also be fully sheathed to provide acorrosion resistant pump in accordance with this invention.

It is a primary object of the present invention to provide an improvedpump for use with corrosive materials wherein the pump chamber is fullysheathed with PTFE.

Another object of the present invention is to provide an improvedcorrosion resistant centrifgual pump having an encapsulated impeller,i.e., one which is fully coated with PTFE.

Another object of the present invention is the provision of acentrifugal pump for corrosive chemical service wherein all portions ofthe wet end of the pump contacted by corrosive liquids are coated with acorrosion resistant coating of PTFE.

Another object of the present invention is the provision of a pump ofthe type described wherein the wet end of the pump chamber is sheathedin PTFE and wherein the sheaths are anchored to prevent movement thereofin response to variations in temperature.

Another object of the present invention is the provision of aself-priming centrifgual pump wherein all fluid contacted surfaces ofthe wet end are sheathed with a corrosion resistant liner of PTFE.

Other objects and advantages of the invention will be apparent from thefollowing description, the accompanying drawings and the appendedclaims.

4 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view in side elevationof a pump in accordance with the present invention;

FIG. 2 is a view in front end elevation of the pump of FIG. 1, lookingfrom the right of FIG. 1;

FIG. 3 is a view partly in section and partly in elevation takengenerally along the line 33 of FIG. 2;

FIG. 4 is an enlarged fragmentary section of the portion of FIG. 3showing the joint between the casing and the rear cover;

FIG. 5A is an enlarged fragmentary section of the seal assembly shown inFIG. 3;

FIG. 5B is an enlarged section of another type of seal assembly usablein accordance with the present invention;

FIG. 6 is a view partly in section and partly in elevation takenessentially along the line 66 of FIG. 3;

FIG. 7 is a view in section taken essentially along the line 77 of FIG.6;

FIG. 8 is a plan view of the discharge end of the P p;

FIG. 9 is a plan view of a PTFE coated impeller in accordance with thepresent invention, with a portion thereof broken away;

FIG. 10 is a side view in section taken along the line 10-10 of FIG. 9;

FIG. 11A is a view in section of the sheath for the casing as formed andbefore assembly thereto;

FIG. 11B is a view in section of the sheath for the rear cover as formedand before assembly thereto;

FIG. 12 is a view partly in section and partly in elevation of aself-priming centrifgual pump in accordance with this invention; and

FIG. 13 is an end view, partly in section and partly in elevation, withportions of the inlet side of the pump removed, of the self-priming pumpin accordance with this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings,which illustrate a preferred form of the invention, FIGS. 1 and 2 show apump 10 operated by a motor 11, the two being interconnected by a driveshaft 12 and a coupling unit 13, the latter connected in drivingrelation to an impeller drive shaft 15. The drive shaft 15 is supportedby a bearing housing 16 containing a. bearing assembly, not shown.

The pump includes a casing 17 and a rear cover assembly 18 which formtherebetween a chamber 20 ,(FIG. 3). In the form shown, the casing 17includes an inlet 2.1 and an outlet 22 each receiving conduits 23 and24, respectively and forming a supply line and a discharge line. Therear cover assembly 18 is secured to the casing 17 by bolts 25. Themotor 11, the bearing unit 16 and casing 17 are individually supportedby feet 26, 27 and 28, respectively, which are bolted to a fixed base 29in the usual way. The bearing housing 16, the internal details of whichare shown in US. Pat. No. 3,169,486 of Feb. 16, 1965, and assigned tothe same assignee, includes a plurality of fingers 30 which are boltedto the rear cover plate 18 by bolts 31.

Referring to FIG. 3, the interior fluid contacted surface portions ofthe casing 17 include a sheath thereon of PTFE which is of sufficientthickness to prevent passage through the sheath of corrosive materials.The sheath 35 includes an integral neck portion 36 extending through theinlet opening 21 and a flared portion 36a engaging a flange 37 on theinlet. As shown, flange 37 includes screw threads and is recevied overthe threaded inlet end of the pump, as shown. The outlet end alsoincludes a flange 38 which receives a flared end 39 of a second integralneck portion 40 (FIG. 6) of the sheath or liner 35 received on thesurface of casing 17.

The rear cover plate 18 is provided with an opening 42 through which thedrive shaft 15 of the impeller extends.

All fluid contacted surfaces of the cover plate 18 are covered with asecond sheath 45 of PTFE which is sufficiently thick to prevent passagetherethrough of corrosive materials. Each of the sheaths or liners 35and 45 include outer peripheral portions 35a and 45a which are in facingrelation and which operate to seal the rear cover 18 to the casing 17.The casing includes an annular undercut 46 (FIG. 4) to form an annularlip 47, the peripheral portion 35a of the sheath being received in theundercut. During assembly of the pump parts the lip 47 aids inmaintaining the peripheral portion 35a in place. The face 49 of thecasing opposite the rear cover includes a series of continuous annularridges and grooves 50 and 51, respectively, which extend all the wayaround the face 49 of the casing. The rear cover plate 18 includes afacing portion 53, positioned opposite the face 49, and having a seriesof continuous annular ridges and grooves 55 and 56, respectively, whichlikewise extend all the way around the facing portion of the rear cover.As shown, the facing portion 53 of the rear cover is of a diameter a fewthousandths of an inch smaller than the radial dimension of the lip forinterfitting relation with the casing.

The differences in height between the grooves and ridges may be as muchas A inch or more depending on the cross-sectional thickness of thesheath and the size of the pump, although such grooves and ridges mayhave a difference in height as small as .005 to .010 of an inch. Thesegrooves and ridges may be interrupted, if desired, although it is easierto form them as continuous elements.

During the assembly of the sheath or liner to the casing and rear cover,the peripheral portions 35a and 45a of the sheaths are forced into thecorresponding grooves allow ing the ridges to bite into the PTFE.Although other forms of securing the peripheries may be used, thisarrangement securely anchors the peripheral portions of both sheaths toprevent movement thereof radially inwardly. Moreover, the pattern ofridges and grooves forms a series of high and low pressure seal areascorresponding to the portions overlying the ridges and those overlyingthe grooves, respectively. By providing a close fitting between the face53 of the rear cover and the face 49 of the casing, extrusion of thePTFE radially outwardly is prevented. The portion of the PTFE overlyingthe grooves is at a lower sealing pressure and functions to pro wide arelief for expansion thereof, as described in US. Pat. No. 3,212,411,issued Oct. 19, 1965, and assigned to the same assignee. Thus, theperipheral portions 35a, 45a of the sheaths are anchored at one end, andin the case of sheath 35, is effectively anchored by securing neckportions 36 and 40 in the inlet and outlet passages by the holdingaction of the corresponding flared portions which are clamped betweenflanges and the associated conduit.

The opening 42 of the rear cover includes an annular shoulder 60 havinga shallow annular counterbore 61 therein. Received in the opening 42between the rear cover 18 and the shaft 15 is a corrosion resistant sealseat 65 which is generally T-shaped in cross-section and which engagesan inner peripheral portion 66 of sheath 45 to force a portion of thesheath into the counterbore 61 for anchoring the inner peripheralportion of the sheath. The annular seal seat 65 is clamped against therear cover by clamp ring 68 which is held in place by studs 69,

annular cushioning gasket 70 being placed therebetween (FIG. A). Theseal seat 65 is of ceramic, tungsten carbide or carbon.

The inner peripheral portion 66 of the sheath is thus clamped andprevented from moving radially inwardly. In this way, both peripheriesof the sheath are held firmly in place to prevent their movement duringtemperature cycling.

Since PTFE has a coefi'icient of thermal expansion greater than mostmetals, provision is made for relief areas in the chamber 20 toaccommodate the growth of the PTFE in response to increases intemperature. Ac-

cordingly, the casing 17 includes on its inner surface a generallyannular relief area into which the PTFE may move or grow thussubstantially preventing permanent deformation as a result of PTFEgrowth due to increasing in temperature. It is to be understood thatother forms of relief areas may be used as will'be apparent to thoseskilled in the art.

Received Within the chamber 20 is an impeller of the open impeller typeand provided with a hollow threaded shank 81 which receives the threadedend of the drive shaft 15, as shown. The outer surface of the im peller80 is coated with PTF-E coating 82 formed over a metal impeller blank 83to form an encapsulated impeller. The outer surface of the blankincludes a PTFE sleeve 84, integral with the coating 82 and extendingover a bearing surface 85 formed on the impeller drive shaft 15.

Referring to FIG. 5A, the shaft 15 is sealed to the rear cover assembly18 by a bellows type seal including a r0- tating annular sealing memberurged into engagement with the sealing face of the annular seal seat 65,of corrosion resistant material, which is clamped in place to the rearcover. The rotatable portion of the seal member is urged into engagementwith the seal seat by a plurality of springs 91 which hear at one endagainst a spring retainer 93 and at the other end against spring adapter94 mounted on a clamp ring 95 secured to the shaft and rotatabletherewith. The sealing member 90 includes PTFE bellows 96, one end 96aof which is clamped to the shaft by ring 95 and the other end 96b ofwhich is secured and sealed to scaling member 90 through a support ring97.'

This type seal structure per se is known.

The seal element 90 prevents passage of fluid between it and the sealseat 65 while the sealed bellows assembly 96 affixed to the rotatingclamp ring 95 prevents passage of fluid between the shaft and end 96a ofthe bellows.

Referring to FIG. 5B, wherein like reference numerals have been employedwhere applicable, a rotatable mechanical seal is shown in which arotating movable seal element 100 is urged into engagement with the sealseat 65 by a plurality of springs 102 through an annular disk 103 whichtends to compress an annular PTFE ring 104 which is generally triangularin cross-section as shown. The rotating portion of this seal is fixed tothe shaft 15 by a compression type coupling 105.

Other forms of seals may be used as will be apparent to those skilled inthe art, for example, double internal mechanical seals, single internalseals, and the like.

Referring to FIGS. 6-8, the pump chamber 20 is in the form of a volutewith all portions of the chamber being covered with a corrosionresistant sheath of polytetrafluoroethylene as indicated previously. Theshank 81 of the impeller receives the threaded end of the impeller shaft15, the shank being covered by a sleeve of PTFE 84 which is integrallyformed with the sheath 82.

The outlet 22 of the pump is formed with a split coupling, one portion106 being integral with the casing and the other 107 being bolted to thecasing by bolts 108. The two parts of the coupling being aligned by pins109 and form the flange which receives the flared portion 39 of thesheath 35. As shown in FIG. 7, a portion of the ridges 50 and groves 51are formed on half coupling 107 and are in alignment with the groovesand ridges formed on the casing.

Referring to FIGS. 9 and 10, the corrosion resistant PTFE encapsulatedimpeller structure 80 is shown. As illustrated, the impeller is of theopen type and includes a metal impeller blank 83, the blank 83 being inthe form of an impeller and including blade elements 110'. All surfacesof the impeller blank are covered with/a PTFE coating 82. The impellerblank also includes a hollow threaded shank 81 with a sleeve portion 84of the PTFE sheath 82 forming a lining which extends beyond the end ofthe shank 81. The sleeve 84 is integral with the sheath 82 but ofsomewhat reduced cross-sectional thickness as shown in FIG. 10.

The sheaths 35 and 45 and the sheath 82 on the impeller are formed by anisostatic coating process, the details of which are described in U.S.patent application Ser. No. 497,869, filed Oct. 19, 1965, now U.S. Pat.No. 3,459,213, and assigned to the same assignee.

Referring to FIGS. 11A and 11B, sheath blanks 115 and 120, correspondingto sheaths 35 and 45, respectively, are formed isostatically in apredetermined configuration corresponding essentially to theconfiguration the respective sheaths have in the assembled pump, as isapparent from comparison of FIGS. 3 and 11A and 11B. Since the sheathblanks are sintered in the configuration shown, they have a primarymemory of this configuration, i.e., this is a stable configuration overquite a range of temperatures. During assembly of the sheaths to thecorresponding pump parts, portions thereof are worked to change theconfiguration slightly from the formed configuration. Specifically,sheath blank 115 is assembled to a casing and portions 116 and 117 areflared to form flanges 36a and 39, respectively. Portion 118 of theblank 115 is flared outwardly, tucked into the undercut 46 to form theouter periphery 35a and pressure is applied to force the PTFE into theridges and grooves as previously described. Since portions 116, 117 and118 of the blank 115 have been worked to change their configuration fromthe predetermined formed configuration, portions 36a, 39 and 35a have asecondary memory of their shape in the casing and a primary memory oftheir formed configuration, as shown in FIG. 11A.

In the case of sheath blank 120, portion 121 is flared outwardly to formthe inner periphery 66 while portion 122 is pressed against face 53 ofthe rear cover to force the PTFE into the ridges and grooves aspreviously described.

Accordingly, the portions of the sheaths 35 and 45 which have beenworked, and which have both primary memory of their formed configurationand a secondary memory of their worked configuration are securelyanchored to prevent changes in configuration due to temperature cycling.It is to be noted, however, that those portions of the sheaths which arecontacted by fluid being pumped have only a primary memory and need notbe locked to the corresponding portions of the casing and rear coverwhen used in the temperature range of -20 F. to +400 F. Thus, byproviding sheaths whose fluid contacted surfaces have a predeterminedformed configuration corresponding to the configuration of the pumpchamber, and thus a primary memory of the predetermined configuration,unusual temperature stability is achieved.

As shown in FIG. 11A, the neck portions 36 and 40 are integral with thesheath blank 115, and the flanges are formed during assembly, as notedpreviously. For this reason, the outlet portion of the pump utilizes asplit coupling, previously described and a threaded flange 37 i on theinlet side, the flange 37 being adjusted so as to engage the flange 36aon the inlet portion of the pump.

The sheath 82 on the impeller is also formed by the isostatic moldingprocedure described in the previously identified application. Here too,sheath 82 has a primary memory of the shape in which it was sintered,that is, essentially the shape of the impeller and therefore exhibitsconsiderable stability to temperature over a wide range.

The advantages of forming the parts isostatically are described fully inU.S. application Ser. No. 497,869, and this procedure offers aconvenient way of forming a sheath on a complex shape. After thesintering operation, the sheaths may be machined to final dimensions, ifneeded, and in the case of sheath 82 formed on the impeller 80, the tipend of the impeller blades and the forward faces 110 are machined tofinal dimensions.

Tests on pumps in accordance with the present invention established thatthe operating parameters were significantly better than originallyanticipated. For example,

an efliciency of 60% for a pump having a three inch diameter inlet and a1% inch diameter outlet end is Percent G.p.1n. elllciency Corrosiontests were also run on pickling solution used to clean stainless steelcastings. This solution is extremely corrosive and cotnains 4%hydrofluoric acid and 20% nitric acid, the solution being at atemperature of 150 F. The pump having the above dimensions and operatingat 1750 r.p.m. and generating a head of 48 feet at about 20 gallons perminute was run for over hours on pickling service. During shut downperiods, the lined pump parts were immersed in the pickling solution forabout 500 hours. The pump was disassembled and examined and showed noappreciable corrosion.

Temperature cycling tests in hot oil established the dimensionalstability of all the parts.

Referring to FIGS. 12 and 13, a self-priming centrifugal pump is shownincluding a priming chamber mounted to the inlet end 21 of the pump andan air separator 137 mounted to the outlet end 22 of the pump, theinternal details of the pump having been previously described.Positioned within the air separator 137 is an air separator tube 138,the air separator 137 and the pump chamber being interconnected by aby-pass line 139. As shown, all internal surfaces of the priming chamberare coated with a corrosion resistant sheath 140 of PTFE, and allinternal surfaces of the air separator 137 are likewise coated with acorrosion resistant sheath 142 except for the air separator tube 138which may be made of corrosion resistant metal.

The priming chamber is formed of two separate castings 144 and 145, thetwo castings being essentially of the same configuration and boltedtogether. The sheaths 140 include flanges 146a and 146b, the castingbeing provided with a priming chamber cover 150 which is clamped insealing relationship through a gasket 151 to an opening 155 formedtherein. As shown, the portion 156 of sheath 140 which covers thepriming chamber cover is likewise flanged to form a seal.

The sheath 142 of the air separator includes a flared end 158 at theexit end of the air separator, and is also flared at the inlet end 159thereof which is connected to the outlet end of the pump. By-pass line139 is in the form of a stainless steel braid covered PTFE line mountedon the by-pass line mounting assembly 160 which likewise includes aflared portion 161 of sheath 142. As shown, the pump chamber includes aby-pass line connection with a side opening 165 formed therein, opening165 including an integral portion 166 of the sheath 35, a flared section167 being provided for sealing purposes between the bypass line and themounting on the chamber.

The casing and rear cover, and the other parts forming the wet end ofthe pump may be of ductile iron or high strength plastic.

The features of the present invention while described with reference toa centrifugal pump may also be used for in-line pumps, positivedisplacement pumps, and the like, in which a pumping element rotateswithin a fully sheathed pump chamber.

It is also understood that while the pump of the present invention isusable as a corrosion resistant pump, it finds use in other fields andservices such as those previously mentioned.

By the present invention, the need for interchangeable wet ends ofdifferent materials in centrifugal pumps is substantially eliminated bythe use of corrosion resistant lining which offers resistance to a widevariety of chemicals. Thus, the metallic elements of the casting neednot be fabricated of the hard to cast materials such as the high siliconiron alloys. The pump of the present invention also exhibits goodperformance characteristics com pared to conventional centrifugal pumps,and superior performance characteristics as compared to centrifugalpumps utilizing a liner of a fluorocarbon copolymer.

While the forms of apparatus herein described constitute preferredembodiments of the invention, it is to be understood that the inventionis not limited to these precise forms of apparatus, and that changes maybe made therein without departing from the scope of the invention.

What is claimed is:

1. In a pump for use with corrosive materials wherein said pump includesa casing and a cover assembly defining therebetween a chamber throughwhich fluid is pumped, a pumping element received within said chamberand cooperating therewith to force fluid through said chamber, driveshaft means extending within said chamber and connected to said pumpingelement for effecting rotation thereof within said chamber, said chamberincluding means communicating therewith and forming an inlet and anoutlet for fluid being pumped, the diameter each of said inlet andoutlet being less than the diameter of said chamber, each of said inletand outlet means including means for connection to conduit means, sealmeans cooperating with said shaft to prevent leakage of fluid betweensaid shaft and said chamber, a first and second polytetrafluoroethylenesheath one covering all fluid contacted surfaces of said casing and theother covering all fluid contacted surfaces of said cover assembly, eachof said sheaths being a unitary structure and said sheaths includingfirst and second neck portions extending respectively through said inletand outlet means, said sheaths and neck portions cooperating to providea chamber and inlet and outlet means fully lined withpolytetrafluoroethylene, said first and second sheath includingcooperating peripheral portions forming a seal therebetween, meanssecuring the peripheral portions of said sheaths against radialmovement, said second sheath including an inner peripheral portionsecured to said cover against radial movement, said sheaths beingsufliciently thick to provide corrosion resistance, and the portion ofeach of said sheaths contacted by fluid being pumped having apredetermined configuration corresponding essentially to theconfiguration in said chamber, the said portion of each said sheathhaving a primary memory of said predetermined configuration. formaintaining said configuration in response to increase in temperature.

2. A pump as set forth in claim 1 wherein said chamber includes meansforming a relief area into which polytetrafluoroethylene may move inresponse to changes in temperature thereby substantially eliminatingpermanent distortion thereof.

3. A pump as set forth in claim 1 wherein the periphera1 portions ofsaid sheaths have a secondary memory.

4. A pump as set forth in claim 1 wherein said pump is a centrifugalpump and wherein said pumping element is an impeller.

5. A centrifugal pump as set forth in claim 4 wherein said first sheathcovers said casing, said second sheath covering said cover assembly,said inlet and outlet means being provided in said casing, and saidfirst and second neck portions being provided in said first sheath.

6. A centrifugal pump as set forth in claim 4 wherein said impellermeans is of a corrosion resistant metal.

7. A centrifugal pump as set forth in claim 5 wherein said impellermeans is encapsulated in polytetrafluoroethylene.

8. A centrifugal pump as set forth in claim 8 wherein said impellermeans includes a shaft section extending through said cover plate, atleast the portion of said shaft section extending through the coverplate including a sheath of PTFE on the outer surface thereof, saidsheath on said shaft section being integral with the sheath on saidimpeller.

9. A centrifugal pump as set forth in claim 9 wherein said coverassembly includes a shoulder formed in the surface thereof opposite saidchamber and surrounding said shaft, the inner peripheral portion of saidsecond sheath being received on said shoulder, stationary seal seatmeans surrounding said shaft and urging the peripheral portion of saidsecond sheath into engagement with said cover assembly, and said sealmeans being mechanical seal means cooperating With said seal seat andshaft to prevent passage therethrough of fluid being pumped.

10. A centrifugal pump as set forth in claim 5 wherein said inlet meansis located in axial alignment with said impeller means, and said outletmeans being located radially of said impeller means.

11. A centrifugal pump as set forth in claim 4 wherein said meanssecuring the peripheral portions of said sheaths includes concentricgrooves formed in the facing peripheral portion of said cover assemblyand said casing, and the peripheral portions of said sheaths includinglands received in said grooves.

12. A pump as set forth in claim 4 wherein said pumping element includesan outer sheath of PTFE on all fluid contacted surfaces thereof.

13. A centrifugal pump as set forth in claim 7 wherein said impellermeans is an open impeller.

14. A centrifugal pump as set forth in claim 4 further including apriming chamber and an air separator, PTFE sheath means covering allfluid contacted surfaces of said priming chamber and said air separator,and corrosion resistant by-pass means interconnecting said chamber andsaid air separator for providing a self-priming pump.

References Cited UNITED STATES PATENTS 2,400,234 5/1946 Hudson 103-1141,578,236 3/1926 La Bour 1031 13 2,466,812 5/ 1949 Jacobsen 1031 132,695,246 11/1954 Jurgensen Jr., et al. l03-114 3,037,458 6/1962Olmstead et al. 103111 3,238,881 3/1966 Camac 1031 14 3,265,002 8/1966Warman 103103 3,358,609 12/1967 Worth et al 103114 FOREIGN PATENTS680,004 2/1964 Canada 415-173 1,092,549 11/1954 France 415-196-1,314,736 12/1962 France 415172 426,523 4/1935 Great Britain 4l5-173885,349 12/1961 Great Britain 415197 HENRY F. RADUAZO, Primary ExaminerU.S. Cl. X.R. 415197, 204

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3,551,067Dated December '29, 1970 Jack L. Wissman Inventor(s) It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 6, line 5, "increasing" should be increases--. Column 6, line 14,"blank" should be shank-.

Column 8, line 20, correct the spelling of "contains". Column 9 line 34,following "chamber," insert the improveme comprising-. Column 10, line5, "claim 5" should be claim 4; line 8, "claim 8" should be claim 7;line 15, "claim 9" should be claim 8; line 25, "claim 5" should be claim4-.

Signed and sealed this 8th day of June 1971.

(SEAL) Attest:

EDwARD-M.FIETGHER,J'R. WILLIAM E. SGHUYLER, J Attesting OfficerCommissioner of Patent

